(1) Field of the Invention
This invention relates to cutter blades for rotary trimmers and more particularly to safety cutter blades made of materials which significantly reduce the risk of injury to operators of such devices and persons in the vicinity thereof.
(2) BACKGROUND OF THE INVENTION
Rotary trimmers of the type with which the instant invention is adapted to be used may be classified in three categories. One is for cutting brush, or brush cutters; a second is for long grass or weeds; and the third is for short grass found in a lawn in positions which a conventional lawn mower cannot reach.
The cutter blades of such trimmers are made of metal and thus present a hazard to operators of such devices as well as people in the vicinity. The recognition of the risk associated with rotary powered mowers and cutting devices has led to the development of safety cutter blades primarily for power lawn mowers. A problem with existing blade designs for rotary trimmers is that when used to cut high grass and weeds, some such designs cause the long grass and weeds to become wound around the shaft rotating the blades which creates a sufficient drag to stall the motor of such trimmers. Blades which tend to prevent long grass and weeds from winding around the shaft are not as effective in cutting short grass when the trimmer is used to trim in places around the lawn which the conventional power mower cannot reach.
To be economically successful, safety trimmer blades must have substantially the same or better performance and useful life as metal blades, be comparable in cost while retaining their safety features. Another characteristic that safety trimmer blades need to successfully compete with conventional blades is a high moment of inertia, to overcome momentarily high resistance to cutting from dense bodies or bunches of weeds or grass. Prior art safety trimmer blades have not been successful in satisfying these criteria.